In order to get forward position (measurement model) of a 6-DOF (six-degrees-of-freedom) parallel-link coordinate measuring machine (CMM)

and overcome the shortcomings of numerical method that the accuracy for the forward kinematics can be influenced easily by the selection of the initial values

an unconstrained optimization model is established and the particle swarm optimization (PSO) algorithm is used for optimizing the model. The unconstrained optimization model of a 6-DOF parallel-link CMM for forward position based on the inverse position model of parallel-link mechanism which is presented. The PSO algorithm is used for solving the optimization problem

and then the forward position can be obtained. The simulation results indicate that 80 particles’ operation precision is about 0.5μm by the 55 times’ operations and the average time is about 3s. The PSO algorithm has the higher speed of calculation and the higher precision for measurement modeling and solution of parallel-link CMM.